Claude Code vs. Claude Cowork: What are the actual under-the-hood differences for a complex dev project?

A developer working on a complex project with the Claude desktop app on Windows is asking for clarification on the differences between Claude Code and Claude Cowork. They have been using Cowork but are considering switching to Code, noting that other threads suggest both modes are similar. The user seeks to understand the actual technical distinctions in features, file handling, tooling, or capabilities, and how their workflows compare in practice for serious development projects.